WO99/61749 Ferguson: “Rock bolt and method of forming a rock bolt” describes indentations forming paddle sections formed by plastically deforming a portion of a steel bar, the deformation made through application of an eccentric shear force on the bar, resulting in paddles such as redrawn in FIG. 8 of the present application. The purposes of Ferguson's rock bolt is for the paddle to enhance mixing, and for the shear formation of the paddle not to plastically deform the bolt axially nor sidewardly of the bolt. Ferguson proposes an expandable shell mounted including radially acting wedges for interacting with the paddles to expand the shells to lock the bolt against the wall of the bolt hole. Ferguson further proposes a plurality of paddle sections formed along the extent of the bolt. A significant disadvantage of the paddles of Ferguson is that the fabricating method involving deforming a portion of the bolt by application of an eccentric shear force, makes the paddle section to constitute the weakest point so that it could not provide a satisfactory anchoring effect.
US-patent application 2005/0158127A1 also to Ferguson, “Yielding strata bolt”, describes a rock bolt having a tendon which may yield by slipping through the anchors rather than by yield of the tendon material, and thereby control movement of unstable rocks into which the bolt is arranged. The tendon as such may be constituted by strands of wire or a metal bar, and has a surrounding tube arranged as a grout slippage mechanism. The grout anchors are constituted by two symmetrical anchor parts clamped to the tendon, please see FIG. 9 of the present application. A disadvantage of US2005/0158127 is the fact that the tension element is only deformed and not strengthened compared to the straight portion of same, and thus the bolt is susceptible to break at the anchor, particularly if the tension element is made of a solid bar. Another disadvantage of US2005/0158127 is the mere number of components required for forming a functioning rock bolt.
German patent DE 35 04 543 defines an anchor rod for being inserted and grouted or glued into boreholes in subsurface cavities. The anchor has an anchor rod with sections having a profiled surface for connection with the rock and a single-ended threaded portion with a nut integral with or welded to the rod itself. The anchor rod has a fixed, integral or welded anchor plate separating between the external threaded portion and the borehole-internal partially profiled portion of the anchor rod and may thus not be used for pre-tensioning the anchor rod in the borehole. A surface profiling of the anchor rod is formed through a wave formation in the longitudinal direction of an originally smooth rod with a round cross-section. The rod of DE 35 04 543 has three consecutive sections for sitting in a borehole: a smooth, projection-free middle portion of the anchor rod with a transition to a wavy portion of the rod in either ends of the smooth middle section, the transition having an increasing wave amplitude in the direction away from the smooth middle section. The smooth portion is for taking up longitudinal forces arising after rock deformation has occurred, but may not prevent initial rock deformation due to the fact that the rock bolt may not be pre-tensioned in the borehole.